In order to meet traffic demands of wireless data which is continuously increasing, the wireless communication system has been developed in a direction for supporting higher data transmission rates. A 4th generation (4G) wireless communication system sought to develop a technology that mainly improves a spectral efficiency to increase the data transmission rate. However, it is difficult to satisfy heavily increasing wireless data traffic demands only with a frequency efficiency improving technology.
Accordingly, research on the use of a very wide frequency band is actively being processed at present. In general, a frequency band currently used for a mobile communication cellular system is equal to or smaller than 10 GHz. Now, it is very difficult to secure a wider frequency band and, accordingly, it is required to secure a broadband frequency in a higher frequency band. However, as the frequency band for wireless communication is higher, a propagation path loss increases and thus a propagation arrival distance becomes relatively short and service coverage becomes reduced. Accordingly, a beamforming technology is currently raised as one of the main technologies to mitigate the propagation path loss and increase the propagation arrival distance.
The beam forming may be classified into transmission beamforming performed at a transmitting end and reception beamforming performed at a receiving end. In general, the transmission beamforming increases directivity by concentrating a radio wave arrival area in a particular direction through a plurality of antennas. At this time, the form in which the plurality of antennas are arranged may be referred to as an antenna array, and each antenna included in the array may be referred to as an array element. The antenna array may be configured in various types, such as a linear array and a planar array. Further, when the transmission beamforming is used, the signal directivity increases and thus a signal transmission distance also increases. In addition, since the signal is hardly transmitted in another direction other than the directed direction, the receiving end gives significantly reduced signal interference to another receiving end.
The receiving end may perform the beamforming on received signals through a reception antenna array. The reception beamforming concentrates reception of radio waves in a particular direction to increase received signal sensitivity incident from the corresponding direction and excludes signals incident from directions other than the corresponding direction from the received signals, so as to provide a gain of blocking an interference signal.
As described above, in order to secure the wide frequency band, an ultra-high frequency, that is, a millimeter wave system is expected to be introduced, in which case the beamforming technology is being considered to overcome the propagation path loss.
However, in the beamforming technology, a base station has to transmit a reference signal in all transmission-available beam directions one or more times and a user equipment has to receive the reference signal in all reception-available beam directions, so that a reference signal transmission efficiency is reduced.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.